1. Field of the Invention
The present invention relates to a rotary cutter which comprises two rolls for holding a workpiece such as fibrous sheet therebetween so as to make cuts in the workpiece only halfway through its thickness from both sides thereof, and also relates to a method for manufacturing a fibrous product using the rotary cutter.
2. Description of the Related Art
Rotary cutters comprising two rolls have been widely used for making a desired pattern of cuts in fibrous products such as a nonwoven fabric, a stack of nonwoven fabrics, a stack of a nonwoven fabric and a fiber bundle layer, etc.
FIG. 9 is a perspective view showing a conventional rotary cutter 1 of this kind.
The rotary cutter 1 comprises a die roll 2 and an anvil roll 3 with their axes arranged parallel with each other. The die roll 2 includes a rotary shaft 4, a periphery 5 formed with a desired radius about the roll axis of the rotary shaft 4, and a plurality of cutting blades 6 projecting radially from the periphery 5. The die roll 2 is provided at its axially opposite ends with contact peripheries 7 and 7, which are formed with a radius slightly larger than the radius of the periphery 5. The cutting blades 6 projects lightly beyond the peripheries 7 and 7 to have their edges located radially outside the peripheries 7 and 7. On the other hand, the anvil roll 3 includes a rotary shaft 8 and a periphery 9 formed with a desired radius about the roll axis of the rotary shaft 8.
In this construction, the distance between the roll axis of the die roll 2 and the roll axis of the anvil roll 3 can be kept constant with the contact peripheries 7 and 7 kept in contact with the periphery 9 of the anvil roll 3. In addition, the cutting blades 6 provided on the die roll 2 can be pressed with desired force against the periphery 9 of the anvil roll 3 by pressing the contact peripheries 7 and 7 against the periphery 9 of the anvil roll 3 with desired force.
When the die roll 2 and the anvil roll 3 are driven to rotate in the directions of the arrows in synchronism with each other and a workpiece W is fed between the die roll 2 and the anvil roll 3, the workpiece W is locally cut by the cutting blades 6 with the workpiece W held between the edges of the cutting blades 6 of the die roll 2 and the periphery 9 of the anvil roll 3.
For example, the workpiece W comprises a substrate sheet Wa such as nonwoven fabric and fiber bundle layers Wb disposed on two sides of the substrate sheet Wa. The fiber bundle layer Wb is a bundle of fibers which individually extend continuously in a feed direction of the workpiece W. In other words, the individual fibers constituting the fiber bundle layer Wb extend in MD without interruption, before cutting with the cutter roller 1. The fiber bundle layers Wb are bonded to the substrate sheet Wa at bond lines Wc which are arranged at regular intervals in the feed direction (MD). When fed between the die roll 2 and the anvil roll 3, the workpiece W is held between the cutting blades 6 and the periphery 9 at positions between adjacent bond lines Wc, whereby the substrate sheet Wa is cut together with the fiber bundle layers Wb, forming cut lines Wd.
Thus, the fiber bundle layers Wb on two sides of the substrate sheet Wa are individually cut into separate portions each of which is fixed to the substrate sheet Wa at one bond line Wc so as to have ends obtained by formation of the cut lines Wd function as free ends. The resulting workpiece W can be used as a cleaning article for wiping the floor and the like, wherein the fiber bundle layers Wb are expected to have an effect of collecting dust like a brush.
In the rotary cutter 1 shown in FIG. 9, however, since the cutting blades 6 project radially beyond the contact peripheries 7 and 7 to have the edges strongly pressed against the periphery 9 of the anvil roll 3 so that the substrate sheet Wa can be cut together with the fiber bundle layers Wb, the edges of the cutting blades 6 tend to generate heat due to high pressure between the cutting blades 6 and the periphery 9. Therefore, if the fiber bundle layers Wb are formed of thermoplastic resin fibers, the fibers constituting the fiber bundle layers Wb may be thermally fusion-bonded to each other or to the substrate sheet Wa along the cut lines Wd.
This results in that the individual fibers constituting the fiber bundle layers Wb are hardly separated from each other in the workpiece W having passed through the cutting process, so that when used as a cleaning article, for example, the fiber bundle layers Wb cannot take on a suitable brush-like form, whereby an expected duct collecting effect cannot be obtained.
In order to prevent the individual fibers constituting the fiber bundle layers Wb from being thermally fusion-bonded to each other along the cut lines Wd, accordingly, the workpiece W may be cut by adopting a so-called half-cut technique in which a workpiece is cut from one side only halfway through its thickness, instead of cutting the substrate sheet Wa and the fiber bundle layers Wb all together under high pressure. In this case, since the cutting force acts on only one of the fiber bundle layers Wb, thermal fusion-bonding between individual fibers can be eliminated or suppressed.
Japanese Unexamined Patent Publication No. 10-76494 discloses such a half-cut technique. In the technique disclosed in the above-identified Patent Publication, the edges of the cutting blades 6 of the rotary cutter shown in FIG. 9 are formed with a radius smaller than the radius of the contact peripheries 7 and 7 so that the blade edges do not come into contact with the periphery 9. When the workpiece W is fed between the die roll 2 and the anvil roll 3, accordingly, the cutting blades 6 penetrate halfway through the thickness of the workpiece W.
However, if the half-cut technique disclosed in the above-identified Patent Publication is adopted to cut the workpiece W shown in FIG. 9, the two fiber bundle layers Wb disposed on two sides of the substrate sheet Wa cannot be cut at once.